The present invention relates, in general, to a bumper structure for a motor vehicle.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
A standard bumper structure is typically mounted on the front or rear of a motor vehicle between the plastic shell construction, which encloses the vehicle body, and the body-supporting structure or chassis of the motor vehicle, and includes a cross member for connection to two longitudinal members of the chassis. To prevent damage to the vehicle structure in the event of a frontal or rear impact at low speed, crumpling or deformation elements, called crash boxes, are arranged between the longitudinal members and the cross member. Crash boxes are thin-walled, normally rectangular elements of steel, aluminum or plastic, and can be manufactured by joining compressed sheet-metal shells or by shaping a single-piece element, e.g. an extruded aluminum section. In the event of an impact, the crash boxes convert the generated kinetic energy into deformation work to prevent permanent damage to the longitudinal members when a critical stress level has been exceeded.
There are many ways to secure the crash boxes to the longitudinal members. Crash boxes may be supported by flanged plates mounted to the end surface of the longitudinal member. The region of the longitudinal member has also an attachment zone to enable a threaded engagement between the components. Thus, there is a need for arrangement of a respective flange. This type of attachment of the crash box requires therefore the provision of additional components so that the overall weight of the motor vehicle is increased.
German utility model no. DE 298 08 143 U1 describes a securement of crash boxes to the longitudinal members on the side by means of transverse bolts. Like the afore-described support of the crash boxes on the end surface of the longitudinal members, this construction too requires increased installation space.
Regardless of the type of attachment of the crash box to the longitudinal member, the provision of tolerance compensating elements, in particular in the form of oblong holes, is necessary. These tolerance compensating elements are normally provided in the flanged plates. Installing crash boxes without flanged plates requires a tolerance compensation between the cross member and the crash box, using complex threaded engagements.
It would therefore be desirable and advantageous to provide an improved bumper structure which obviates prior art shortcomings and is compact and lightweight so as to utilize the available installation space upon the longitudinal members in an optimum manner while reliably compensating tolerances in the attachment zone between the longitudinal members and the crash boxes.